[Qemu-devel] [PATCH 06/13] Threadlet: Add dequeue_work threadlet API

[Arun R Bharadwaj <arun@linux.vnet.ibm.com>]

This patch adds dequeue_work threadlet API and shows how
the paio_cancel changes to dequeue_work.

Signed-off-by: Arun R Bharadwaj <arun@linux.vnet.ibm.com>
---
 posix-aio-compat.c |   46 ++++++++++++++++++++++++++--------------------
 1 files changed, 26 insertions(+), 20 deletions(-)

diff --git a/posix-aio-compat.c b/posix-aio-compat.c
index ff6e08b..8f1a9b6 100644
--- a/posix-aio-compat.c
+++ b/posix-aio-compat.c
@@ -574,33 +574,39 @@ static void paio_remove(struct qemu_paiocb *acb)
     }
 }
 
-static void paio_cancel(BlockDriverAIOCB *blockacb)
+/**
+ * dequeue_work: Cancel a task queued on the global queue.
+ * @work: Contains the information of the task that needs to be cancelled.
+ *
+ * Returns: 0 if the task is successfully cancelled.
+ *          1 otherwise.
+ */
+static int dequeue_work(ThreadletWork *work)
 {
-    struct qemu_paiocb *acb = (struct qemu_paiocb *)blockacb;
-    int active = 0;
+    int ret = 1;
 
     qemu_mutex_lock(&globalqueue.lock);
-    if (!acb->active) {
-        QTAILQ_REMOVE(&globalqueue.request_list, &acb->work, node);
-        acb->ret = -ECANCELED;
-    } else if (acb->ret == -EINPROGRESS) {
-        active = 1;
-    }
+    QTAILQ_REMOVE(&globalqueue.request_list, work, node);
+    ret = 0;
     qemu_mutex_unlock(&globalqueue.lock);
 
-    qemu_mutex_lock(&aiocb_mutex);
-    if (!active) {
-        acb->ret = -ECANCELED;
-    } else {
-        while (acb->ret == -EINPROGRESS) {
-            /*
-             * fail safe: if the aio could not be canceled,
-             * we wait for it
-             */
-            qemu_cond_wait(&aiocb_completion, &aiocb_mutex);
+    return ret;
+}
+
+static void paio_cancel(BlockDriverAIOCB *blockacb)
+{
+    struct qemu_paiocb *acb = (struct qemu_paiocb *)blockacb;
+    if (!acb->active) {
+        if (dequeue_work(&acb->work) != 0) {
+            /* Wait for running work item to complete */
+            qemu_mutex_lock(&aiocb_mutex);
+            while (acb->ret == -EINPROGRESS) {
+                qemu_cond_wait(&aiocb_completion, &aiocb_mutex);
+            }
+            qemu_mutex_unlock(&aiocb_mutex);
         }
     }
-    qemu_mutex_unlock(&aiocb_mutex);
+
     paio_remove(acb);
 }